1. Field of the Invention
The present invention relates to display device fabrication, and more particularly to an apparatus and it fabrication methods which employ modular active devices which are separately fabricated from and assembled on a substrate.
2. Description of the Related Art
Flat panel displays, such as OLEDs (Organic Light Emitting Diodes) or AMLCDs (Active Matrix Liquid Crystal Displays), are currently manufactured in a process where the light emitting or transmitting elements are built simultaneously with active electrical devices and addressing electrodes. All these elements are formed in their final desired position on a common substrate. These active electrical devices are formed at each subpixel element of an array of subpixels. This approach has significant economic in that the processing required for fabrication of the active electrical devices is much more complex than that required for fabrication of the pixel electrode for light emitting or transmitting elements and the addressing electrodes.
In one example, a passivated amorphous silicon thin film transistor (TFT) can be formed in four mask steps, and if the addressing lines do not include cross-overs and passivation is not required, then only two mask steps are required to pattern aluminum conductors and transparent Indium Tin Oxide (ITO) pixel electrodes for the light emitting or transmitting elements. In a typical direct view OLED or AMLCD display, the active electrical devices only occupy about 10% or less of the total substrate area.
Significant cost savings could be achieved if the active electrical devices could be fabricated separately from the substrate including the pixel electrodes and the addressing electrodes, and subsequently assembled onto the substrate including the pixel and the addressing electrodes if a low cost and compact joining technology was used.
One approach for assembling small pieces of silicon chips containing the active electrical devices onto a display substrate is fluidic self assembly described by Alien Technologies (See, Alien Technology Corporation White Paper, xe2x80x9cFluidic Self Assemblyxe2x80x9d, October 1999). In this process, the display substrates are formed from plastic and include indentations where it is desirable to locate active electrical devices. The indentations match the shape of the small pieces of silicon chips. The small chips are suspended in a fluid which flows over the substrate and deposits the chips in the desired locations. Electrical connections are formed by depositing metal over the chips including the active electrical devices and the substrate and patterning the metal. This approach has significant disadvantages in that the indentations in the substrate and the small chips including the active electrical devices must be precisely shaped to match and there is no easy means of replacing the small chip including the active devices or reworking the electrical contact to the substrate if a small chip including the active devices is damaged during assembly and processing or an electrical contact fails.
Further, the precise shape of the small silicon chip including the active devices is achieved by photolithography in combination with anisotropic etching of: single crystalline silicon, so expensive silicon wafers must be used for fabrication of the active devices.
Therefore, a need exists for an apparatus and method of fabrication which includes separately fabricated active devices integrated on a substrate for a display device for reducing costs and manufacturing complexity.
A method for fabricating a display device patterns a conductive layer on a display substrate and forms pixel electrodes on the display substrate. A plate is employed for carrying separately fabricated devices to the display substrate. The separately fabricated devices are connected to the conductive layers and the pixel electrode.
Another method for fabricating a display device, in accordance with the present invention includes the steps of providing a first substrate having chiplets formed in a pattern on a parting layer, attaching a first plate to a top side of the chiplets, separating the chiplets from the first substrate at the parting layer, attaching a back side of selected chiplets to a second plate and aligning and connecting the front side of the selected chiplets to a display substrate.
In other methods, the separately fabricated devices preferably include chiplets. The chiplets may include a transistor and/or a capacitor. The chiplets may include a cross-over connector which provides a connection between conductors formed on the display substrate. The method may include the steps of forming conductive attachments on the display substrate and the separately fabricated devices and aligning and connecting the separately fabricated devices with the display substrate by the conductive attachments. In still other embodiments, the conductive attachments on one of the display substrate and the separately fabricated devices may include at least one of solder bumps, conductive adhesive bumps and thermocompression bond pads. The plate carrying separately fabricated devices may include holes, and the method may further include the step of applying vacuum through the holes to carry the separately fabricated devises. The step of patterning a conductive layer on a display substrate may include patterning gate lines and data lines from the conductive layer. The method may include the step of removing a separately fabricated device from the display substrate. The method may include the step of disengaging the separately fabricated devices from the plate.
A display device includes gate lines and data lines patterned from a single layer of conductive material. Pixel electrodes are formed in operative relationship with the gate lines and data lines. A plurality of chiplets are connected to the gate lines, the data lines and the pixel electrodes such that the chiplets activate the pixel electrodes in accordance with the gate lines and the data lines.
In other embodiments, the display device may include an active matrix liquid crystal display or an organic light emitting diode display. The plurality of chiplets may be connected to the gate lines, the data lines and the pixel electrodes by conductive attachments. The conductive attachments may include at least one of solder bumps, conductive adhesive bumps and thermocompression bond pads. The plurality of chiplets may provide a cross-over connection between data lines. The chiplets may each include a transistor which is connected to at least a data line and a gate line. The chiplets may each include a storage capacitor. The chiplets may include a size related to a fraction of sub-pixel size for sub-pixels of the display device.